PFT FOR ADULT AND PEDIA

PFT FOR ADULT AND PEDIA OverviewPulmonary Function Testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, chest x-ray examinations, arterial blood gas analysis, and test of pulmonary function.The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment. Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease.

Purpose of PFTTo measure the different lung volumes and capacities.To distinguish the cause of abnormal gas measurements.To evaluate surgical risks.To detect the early manifestation of pulmonary disease.To differentiate primary causative abnormalities.To evaluate disability for medical reasons.

Indications of PFTIs indicated anytime than an assessment of the respiratory system is required or desired. Specifically, PFT will evaluate the:Presence of lung disease.Extent of abnormal lung function.Amount of disability due to the dysfunction.Progression of the disease.Response to therapy.

Tidal Volume (VT = 500ml) - The volume of air routinely inhaled or exhaled during normal respiration.Inspiratory Reserve Volume (IRV = 3000ml) maximum volume of air inspired from the end of the normal VT inspiration. Expiratory Reserve Volume (ERV = 1000ml) maximum volume of air exhaled from the resting expiratory levelResidual Volume (RV = 1500ml) air remaining in the lungs after maximum expiration.

Lung Volumes LUNG CAPACITIESAre combinations of two or more primary lung subdivisionsInspiratory Capacity (IC = 3500ml) = VT + IRV Maximum volume of air that can be inhaled after a normal exhalation.Functional Residual Capacity (FRC = 2500ml) = ERV + RV Volume of air that remains in the lungs after a normal exhalation.Vital Capacity (VC = 4500ml) = VT + IRV + ERVMaximum volume of air that can be exhaled after a maximum inspirationTotal Lung Capacity (TLC = 6000ml) = VT + RV + IRV + ERVVolume of air contained in the lungs at maximum inhalationLung Volume Compartments and Subdivision

SPIROMETRY

Means the measuring of breathThe most commonly performed among the Pulmonary Function TestMeasures lung function, specifically the measurement of the amount (volume) and/ or speed (flow) of air that can be inhaled and exhaled.An important tool used for assessing conditions such as asthma, Cystic Fibrosis and COPD

Forced Vital Capacity (FVC) The volume of air that is forcefully exhaled after a maximum inhalation is performed. FEV 0.5 the volume of air exhaled during the first one-half second of exhalation.FEV1 the volume of air exhaled during the first second of an FVC maneuver.FEV3 the volume of air exhaled during an FVC maneuver in three seconds FEV1/FVC A parameter to use to distinguish obstructive pulmonary disease from restrictive pulmonary/normal conditionsSpirometric Parameters FEF 25-75% - Forced Expiratory Flow Rate between 25 and 75%.- average flow rate during the mid-portion of the FVC.- decreased in the early stages of obstructive diseases.- decreased values are associated with small airway obstruction. FEF 75-85% - Forced Expiratory Flow at 75-85%.- the flow rate between 75-85% of the vital capacity. FEF 200-1200 Force Expiratory Flow Rate between 200ml and 1200ml.- average flow during the first 1000 ml after 200ml expired.- decreased values are associated with large airway obstruction.- typical value: 8 L/sec (480 L/min.) Peak Expiratory Flow Rate (PEFR)- effort dependent and may appear normal in abnormal patients.- sometimes used to evaluate asthmatic patients, pre and post bronchodilation.- typical value: 10 L/sec. (600ml)

FLOW VOLUME LOOP A graphical representation of flow plotted against volume during FVC maneuverUpper 25% of the curve flow reflects expiratory muscle strengthGradual decline in flow back to zero Inspiratory loop deep curve plotted on the negative portion of the flow axis

Normal Spirometry

Obstructive PatternReduced FEV1 disproportionately more than FVCExpiratory curve descends quicker, concave shapeFEV1/FVC < 70%

Common Obstructive DiseasesAsthmaAsthmatic bronchitisChronic obstructive bronchitisChronic obstructive pulmonary disease (COPD includes asthmatic bronchitis, chronic bronchitis, emphysema and the overlap between them).Cystic fibrosisEmphysema

Restrictive

- Size of flow -volume loop is relatively smaller - FVC and TLC reducedCommon Restrictive DiseasesIdiopathic pulmonary fibrosisInterstitial pneumonitisInfectious inflammation (eg, histoplasmosis, mycobacterium infection)Thoracic deformitiesCongestive heart failureNeuromuscular diseases

Performance of FVC maneuverCheck spirometer calibration.Explain test.Prepare patient.Ask about smoking, recent illness, medication use, etc.

Performance of FVC maneuver (continued)Give instructions and demonstrate:Show nose clip and mouthpiece.Demonstrate position of head with chin slightly elevated and neck somewhat extended.Inhale as much as possible, put mouthpiece in mouth (open circuit), exhale as hard and fast as possible.Give simple instructions.

Performance of FVC maneuver (continued)Patient performs the maneuverPatient assumes the positionPuts nose clip onInhales maximallyPuts mouthpiece on mouth and closes lips around mouthpiece (open circuit)Exhales as hard and fast and long as possibleRepeat instructions if necessary be an effective coachRepeat minimum of three times (check for reproducibility.)

Special Considerations in Pediatric PatientsAbility to perform spirometry dependent on developmental age of child, personality, and interest of the child.Patients need a calm, relaxed environment and good coaching. Patience is key.Even with the best of environments and coaching, a child may not be able to perform spirometry. (And that is OK.)

Maximum Voluntary VentilationFormerly called maximum breathing capacity (MBC)Effort dependentPatient performs deep and fast breathing for 12 seconds and the value of MVV is extrapolated for the resultEvaluation of ventilatory reservesNV: 150-200 L/min

Infant Pulmonary Function Test

Infant pulmonary function testing (iPFT) is a way to measure the breathing of babies and toddlers.The test is done by having your child breathe in a special machine to take measurements of how much air is in his or her lungs.The iPFT is done under sedation. That means that your child will receive medication to make him or her sleep through the test.

Pulmonary function tests measure how well your childs lungs are working. They measure how fast air can flow through the airways, how much air is in the lungs and how stiff the lungs are. This information is important in diagnosing breathing problems and checking to see if current treatments are working. The results of these tests can show if your childs lungs or airways are obstructed (blocked) in any way because of asthma or other conditions that affect breathing.In older children who are able to follow instructions, lung function is checked through a test called spirometry, which measures breath capacity as a child blows out into a tube. When children are too youngor are unableto follow instructions, lung function is measured with infant pulmonary function testing (iPFT). iPFT uses special equipment to measure lung function while the child is asleep. iPFTs are very safe and can be performed even on tiny babies.Infant Pulmonary Function Testing Procedure:Your child will be given medication by mouth to make him or her drowsy. This medication takes effect in about 15 to20 minutes. You may stay with your child as he or she falls asleep and throughout the entire test.After your child falls asleep, he or she will be placed into a clear plastic device in which the lung measurements will take place.A thin strip of medical putty, will be rolled into a cigar shape and pressed around the edge of a soft plastic mask, which will be placed over your childs mouth and nose. The putty will create an airtight seal and give the mask a custom fit to your childs face.

The mask will be connected to a computer, which will measure the airflow. As your child breathes into the mask, the computer will measure how much air is in your childs lungs.A vest will be wrapped around your childs chest. The vest will inflate very quickly to give your childs chest a hug that will help your child blow all the air out of the lungs. Before the hug, the doctor may inflate the lungs with extra air through the mask. The computer will measure how fast air can flow into and out of your childs lungs.Your child will be given a breathing treatment, such as albuterol, through the mask to open your childs lungs and breathing tubes. The tests will be repeated to measure improvement.The breathing tests will not hurt your child.

Example of Spirometers Portable Spirometer PC Based Spirometer

COMPLETE PFT MACHINE

Nitrogen Wash-out, Open Circuit MethodThis method involves having the subject breathe 100% O2, beginning at the resting expiratory level during normal breathing. At start, the FRC contained 80% nitrogen (N2).The subject breathes 100% O2 until all N2 has been washed out of the lung and replaced by O2. When all N2 in the lungs has been replaced by O2, total volume of gas is collected and measured (a) actual amount of N2 is found (b) actual FRC can be calculated. The RV is calculated by subtracting the spirometry-determined ERV from the FRC: RV = FRC ERVThe TLC is calculated by adding the VC to the RV: TLC = RV + VC

Helium Dilution Closed Circuit Equilibration MethodInvolves starting with a known amount of Helium with the spirometer.The subject breathes Helium until the lungs and spirometer reach equilibrium.The beginning Helium concentration in the lung is zero.With the known starting volume of gas and Helium concentration in the spirometer and the new Helium concentration after equilibrium, the starting lung volume can be calculated.

Plethysmographic Method or Body BoxUsing Boyles Law to determine total thoracic gas volume at FRC.Measures gas trapped inside the lung and otherwise excluded from the FRC with the other procedure (He dilution and N2 washout).Airway resistance (Raw) can be determined by measuring the volume change per unit pressure change in liters/cmH20 or milliliters/cmH20 (Normal Compliance = 60-100 Ml/cmH20).Advantage: it will more accurately measure FRC in patients with obstructive lung disease. Disadvantages: (a) patient may be unable to enter the box due to physical limitations (b) claustrophobia prohibits patient from entering box (c) patient may be unable to pant acceptably.Rapid, accurate, good for disease cases, but equipment is expensive.